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| United States Patent |
5,110,780
|
|
Peters
|
May 5, 1992
|
Carbon monoxide oxidation catalyst
Abstract
A carbon monoxide oxidation catalyst especially useful as a co-catalyst in
fluid catalytic cracking operations is made by impregnating particulate
alumina with lanthana and a small amount of platinum. Cerium must be
excluded.
| Inventors:
|
Peters; Alan W. (Rockville, MD)
|
| Assignee:
|
W. R. Grace & Co.-Conn. (New York, NY)
|
| Appl. No.:
|
531197 |
| Filed:
|
May 31, 1990 |
| Current U.S. Class: |
502/303 |
| Intern'l Class: |
B01J 021/04; B01J 023/10 |
| Field of Search: |
502/303,65
423/437
|
References Cited
U.S. Patent Documents
| 3993572 | Nov., 1976 | Hindin et al. | 252/462.
|
| 4140655 | Feb., 1979 | Chabot et al. | 252/462.
|
| 4170573 | Oct., 1979 | Ernest et al. | 252/462.
|
| 4259212 | Mar., 1981 | Gladrow et al. | 208/120.
|
| 4292288 | Sep., 1981 | Gladrow | 423/437.
|
| 4483764 | Nov., 1984 | Hensley, Jr. et al. | 208/111.
|
| 4528279 | Jul., 1985 | Suzuki et al. | 502/200.
|
| 4722920 | Feb., 1988 | Kimura et al. | 502/303.
|
| 4738946 | Apr., 1988 | Yamashita et al. | 502/303.
|
| 4755498 | Jul., 1988 | Setzer et al. | 502/303.
|
| Foreign Patent Documents |
| 2094657 | Oct., 1985 | GB.
| |
| 2140791 | Oct., 1985 | GB.
| |
Other References
H. Schaper et al, "The Influence of Lanthanum Oxide on the Thermal
Stability of Gamma Alumina Catalyst Supports", Applied Catalysis, 7 (1983)
211-220.
|
Primary Examiner: Dees; Carl F.
Attorney, Agent or Firm: Savage; Arthur P.
Parent Case Text
This is a continuation of Ser. No. 231,327, filed Aug. 12, 1988, abandoned.
Claims
I claim:
1. A carbon monoxide catalyst composition for use in fluid catalytic
cracking processes comprising about 4 to 30 weight percent lanthana and
about 50 to 1000 ppm platinum on an alumina substrate having a surface
area of about 45 to 450 m.sup.2 /g, said catalyst being cerium free and
having an average particle size of about 20 to 200 microns.
2. The composition of claim 1 wherein lanthana is about 4-8 weight percent,
platinum is about 200-800 ppm, and substrate surface area is about 60-200
m.sup.2 /g.
3. The composition of claim 2 wherein lanthan is about 8 percent, platinum
is about 500 ppm, and substrate surface area is about 130 m.sup.2 /g.
4. The composition of claim 1, 2, or 3, formed into microspheroidal
particles.
5. A method of making the carbon monoxide oxidation catalyst of claim 1
comprising impregnating a finely divided alumina substrate having a
particle size of about 200 to 210 microns with a cerium-free solution of a
lanthanum compound and a solution of a platinum compound, and drying and
calcining the impregnated substrate.
6. The method according to claim 5 wherein the substrate is impregnated
with a solution which contains both lathanum and platinum compounds.
7. The catalyst of claim 1 having a particle size of about 40 to 120
microns.
Description
RELATED APPLICATION
U.S. patent application Ser. No. 936419 filed 1 Dec. 1986, owned by the
same assignee hereof, discloses and claims a sulfur oxide gettering
composition comprising a lanthana-alumina complex on an alumina substrate.
The La-alumina complex may be distributed on the complex in combination
with a platinum-containing carbon monoxide oxidation agent.
FIELD OF THE INVENTION
The present invention relates to carbon monoxide oxidation catalyst
compositions and their use.
More specifically the invention contemplates the preparation and use of
novel highly efficient catalytic compositions which may be used to control
carbon monoxide emissions from a variety of sources, and especially in
fluid cracking catalysis (FCC).
The new catalyst compositions comprise platinum and lanthanum oxide
deposited on finely divided alumina of a specific type, in specific
amounts and manner.
PRIOR ART
U.S. Pat. No. 3993572 discloses an alumina monolith, e.g., for an auto
exhaust, treated with rare earths generally, and Ce in particular, plus
Pt.
U.S. Pat. No. 4140655 discloses an alumina monolith, e.g., for an auto
exhaust, treated with 1-3 percent La, plus Pt and Rh.
U.S. Pat. No. 4170573 discloses an auto exhaust alumina monolith treated
with Ce plus La plus Pt.
U.S. Pat. No. 4528279 discloses an auto exhaust alumina monolith treated
with La and Pt.
U.S. Pat. No. 4722920 discloses La on alumina auto exhaust monolith.
U.S. Pat. No. 4738946 discloses oxidation catalysts which comprise
catalytically active metals such as palladium supported on a
lanthanum-beta alumina substrate.
U.K. Patents 2094657 and 2140791 disclose petroleum cracking catalysts
which are used to control SOx emissions that contain a lanthana alumina
additive which may also include an oxidation catalyst such as platinum.
H. Schaper et al, Applied Catalysis, 7 (1983) 211-220, describes the
preparation of lanthana/alumina catalyst supports.
BACKGROUND OF THE INVENTION
Cracking catalysts which are used to crack hydrocarbon feedstocks become
relatively inactive due to the deposition of carbonaceous deposits on the
catalyst. These carbonaceous deposits are commonly called coke. After the
cracking step, the catalyst passes to a stripping zone where steam is used
to remove strippable hydrocarbons from the catalyst. The catalyst then
goes to the regenerator, where the catalyst is regenerated by burning the
coke in an oxygen-containing gas. This converts the carbon and hydrogen in
the coke to carbon monoxide, carbon dioxide and water.
Oxidation catalysts are currently being used in fluid catalytic cracking
(FCC) combustion units to oxidize CO to CO.sub.2 in the catalyst bed
during the coke-burning step in the regenerator. Typically the oxidation
catalysts are particulate combustion additives that contain 100 to 1000
ppm Pt and/or Pd supported on alumina. The combustion additives are mixed
with FCC catalysts in amounts that provide a Pt/Pd content of about 0.1 to
2 ppm and preferably about 0.1 to 0.8 ppm. The oxidation of CO to CO.sub.2
in the catalyst bed yields many benefits. One benefit is the reduction of
CO emissions. Another is the avoidance of "after-burning", i.e., the
oxidation of CO to CO.sub.2 outside the catalyst bed, which results in a
loss of heat energy and causes damage to the cyclones and flue gas exit
lines. The major benefit in using oxidation catalysts to oxidize CO to
CO.sub.2 in the catalyst regenerator bed derives from the heat released
when the CO is oxidized to CO.sub.2. This heat raises the catalyst bed
temperature and thereby increases the coke-burning rate. This gives a
lower residual carbon level on the regenerated catalyst. This, in turn,
makes the regenerated catalyst more active for the cracking step. This
increases the amount of useful products produced in the FCC unit.
CO oxidation catalysts (also referred to herein as agents, additives,
promoters, compositions, etc.) when intended for use in FCC units, must of
course be compatible under the actual conditions used in FCC units and
must remain effective for their subsequent function in the regeneration
step. Such FCC units conventionally require temperatures of
800.degree.-1000.degree. F. (427.degree.-538.degree. C.) and catalyst
residence times of 3 to 15 seconds in the reducing atmosphere of the
reactor; followed by temperatures of 800.degree.-1000.degree. F.
(427.degree.-538.degree. C.) in the steam atmosphere of the stripper and
temperatures of 1100.degree.-1400.degree. F. (593.degree.-760.degree. C.)
and catalyst residence times of 5 to 15 minutes in the oxidizing
atmosphere of the regenerator. Additionally, CO oxidation agents for use
in FCC units must be effective in the presence of the materials present in
FCC units, such as cracking catalysts of various compositions and oil
feedstocks of various compositions and their cracked products. My novel CO
oxidation agents are useful in and compatible with all these FCC
conditions.
OBJECTS
It is an object of the present invention to provide a carbon monoxide
oxidation catalyst which is active over a long period of time when
subjected to multiple regeneration cycles. These catalysts may be used in
cracking catalyst compositions which effectively and economically reduce
the emission of carbon monoxide from FCC units.
It is a further object to provide a carbon monoxide oxidation additive
which may be added to the catalyst inventory of an FCC unit in amounts
necessary to reduce carbon monoxide regenerator stack gas emissions to an
acceptable level.
It is still a further object to provide a highly effective carbon monoxide
oxidation agent which may be advantageously combined with conventional
cracking catalyst compositions or used to control carbon monoxide
emissions from a variety of processes.
These and still further objects will become apparent to one skilled in the
art from the following detailed description and specific examples.
THE INVENTION
Broadly stated, my invention contemplates an improved carbon monoxide
oxidation catalyst which comprises an alumina (Al.sub.2 O.sub.3) substrate
having a surface area of at least 45 M.sup.2 /g and 4 to 30 percent by
weight lanthanum oxide (La.sub.2 O.sub.3) uniformly distributed on the
surface of the alumina substrate. To this lanthana-alumina is added
50-1000 ppm platinum.
In practice, I prefer about 4-8 weight percent La.sub.2 O.sub.3 and about
200-600 ppm Pt combined with an alumina substrate which has a surface area
of 45 to 450 m.sup.2 /g, preferably 60-200 m.sup.2 /g. My combustion
additives may be mixed with conventional FCC catalysts in amounts which
provide a Pt concentration of about 0.1 to 2 ppm and preferably about 0.1
to 0.8 ppm. I use alumina with an average particle size in the range of
about 20-200 microns, preferably about 40-120 microns.
Suitable particulate alumina substrates are available from many commercial
sources, and comprise the alumina hydrates, such as alpha alumina
monohydrate, alpha alumina trihydrate, beta alumina monohydrate, and beta
alumina trihydrate. Also suitable are the calcined versions of the above
alumina hydrates. These include gamma alumina, chi alumna, eta alumina,
kappa alumina, delta alumina, theta alumina, alpha alumina, and mixtures
thereof. In a preferred embodiment, the alumina substrate is in the form
of microspheroidal particles, with about 90 percent of the particles
having diameters in the 20 to 149 micron fluidizable size range. The CO
oxidation agent prepared using these microspheroidal particles may be
advantageously physically mixed with FCC catalysts in amounts which
provide a Pt content of about 0.1 to 5.8 ppm.
A particularly useful substrate is Condea alumina, a gamma alumina of about
120 m.sup.2 /g surface area, available commercially from Condea, a German
company.
In another preferred embodiment, the alumina substrate is in the form of
particles which have an average particle size of less than 20 microns in
diameter, and preferably less than 10 microns in diameter. The finished
agent prepared using these fine particles may be incorporated in a
cracking catalyst composition during the formation of the catalyst
particles.
The Lanthanum Oxide Component
The lanthanum oxide component which is impregnated onto the alumina surface
may be obtained as a commercially available lanthanum salt such as
lanthanum nitrate, chloride, or sulfate. The lanthanum compound should be
substantially free of cerium. In the presence of an adequate amount of
La.sub.2 O.sub.3, say about 6-8 percent, 2 percent Ce is useless. It is
actually harmful if the La.sub.2 O.sub.3 is less.
The Platinum Component
Various compounds, complexes, or elemental dispersions of platinum in
aqueous or organic media may be used to deposit platinum on the
lanthana-alumina composite. In addition to (NH.sub.4).sub.6
Pt(SO.sub.3).sub.4, used in the examples, suitable Pt compounds include
chloroplatinic acid; potassium platinum chloride; ammonium platinum
thiocyanate; platinum tetrammine hydroxide; platinum oxide, sulfide,
nitrite, or nitrate; platinum tetrammine chloride; and the like. The
impregnation solution is preferably an aqueous solution containing about
0.2 moles of Pt/100 g solution.
Formation of CO-Oxidation Promoter
To prepare my novel carbon monoxide oxidation agent, the alumina substrate
is uniformly and thoroughly admixed with a quantity of lanthanum salt
solution which will provide the desired uniform dispersion of lanthanum
oxide on the alumina surface. Typically, the soluble lanthanum, preferably
lanthanum nitrate, is dissolved in water to provide a desired volume of
solution which has the desired concentration of the lanthanum salt. The
alumina substrate is then impregnated, as uniformly as possible, with the
lanthanum salt solution to give the desired amount of lanthanum on the
alumina. The impregnated alumina is then calcined at a temperature
sufficient to decompose the lanthanum salt and fix the resulting lanthanum
oxide uniformly onto the alumina surface. While it is contemplated that
calcination temperatures of up to about 1500.degree. F. (816.degree. C.)
may be used, calcination temperatures on the order of 1000.degree. F.
(538.degree. C.) have been found to be satisfactory. These same
calcination temperatures apply to calcination following platinum
deposition.
Platinum is now impregnated on the calcined lanthana-alumina composition,
as above described. The Pt-La-alumina composite is then dried. Under
certain circumstances, e.g., for test purposes, the composite may be
activated by reducing in flowing hydrogen at about 900-1350 for 0.1-4
hours, suitably 950.degree. F. for 3 hours, cooling, then calcining for 6
hours at 1350.degree. F. in 50 percent air and 50 percent steam.
The CO-oxidation agent may also be prepared by co-impregnation of the
alumina support with a solution which contains both the desired quantity
of lanthanum and platinum salts, followed by drying and calcining as
indicated above.
Although the CO-oxidation agent of this invention may be used by itself to
reduce CO emissions from a variety of processes, it is particularly useful
in combinative use with FCC catalysts.
Combined CO-Oxidation Agent/FCC Catalysts, Etc.
The CO oxidation agent of this invention may be used as a separate additive
which is added to the base FCC catalyst as a separate particulate
component, or the agent may be combined with the base FCC catalyst during
the preparation of the latter to obtain catalyst particles which contain
the CO oxidation agent as an integral component. For example, the
La-Pt-impregnated alumina may be added to an aqueous slurry of FCC
catalyst components, followed by spray drying.
The same type of integration may be used with base catalysts other than
cracking catalysts.
Cracking catalysts which may be advantageously combined with the CO
oxidation agent of the present invention are commercially available
compositions and typically comprise crystalline zeolites admixed with
inorganic oxide binders and clay. Typically, these catalysts comprise from
about 5 to 50 percent by weight crystalline aluminosilicate zeolite in
combination with a silica, silica-alumina, or alumina hydrogel or sol
binder and optionally from about 10 to 80 percent by weight clay. Zeolites
typically used in the preparation of cracking catalysts are stabilized
type Y zeolites.
The instant CO-oxidation agents may be combined with a cracking catalyst
which comprises an alumina sol, i.e., aluminum chlorhydroxide solution,
bound zeolite/clay composition, thereby giving a composition which
comprises, e.g., 0.5 to 60 percent by weight CO oxidation agent and the
balance cracking catalyst.
In another preferred practice, my CO oxidation agent is combined with a
zeolite cracking catalyst which possesses an essentially silica-free
matrix. These catalysts are obtained by mixing together the following
materials: 5 to 50 weight percent zeolites, 10 to 80 weight percent
alumina hydrate (dry basis), and 5 to 40 weight percent aluminum
chlorhydroxide sol (Al.sub.2 O.sub.3), and water. The mixture was
spray-dried to obtain a finely divided catalyst composite and then
calcined at a temperature of about 1000.degree. F. (538.degree. C.). My CO
oxidation agent may be included as a component in the spray dried slurry
in lieu of some of the alumina hydrate, or the agent may be physically
blended with the catalyst in the amount of 0.5 to 60 weight percent.
My CO oxidation agent catalyzes the oxidation of CO to CO.sub.2 (in the
presence of air or oxygen) suitably at a temperature in the range of about
1100.degree.-1500.degree. C.
In sum, my CO oxidation agent may be used by itself, apart from other
catalysts, or it can be blended with other catalysts in various ways. For
example, it may be physically blended with another catalyst, or it may be
incorporated into the catalyst particle of the other catalyst by adding it
to the other catalyst as the other is being formed.
My CO-oxidation agent, following loss of activity due to prolonged use, may
be restored or regenerated by reduction and/or hydrolysis in the presence
of a reducing gas and/or steam. Following regeneration, the agent may be
returned to the CO-oxidation zone. When the agent is a component of a base
cracking catalyst, the cracking catalyst composite may be similarly
recycled to the reaction zone.
Having described the basic aspects of my invention, the following examples
are given to illustrate specific embodiments thereof.
EXAMPLE 1
A sample of gamma-alumina (Condea) of 40-150 micron particle size and 129
m.sup.2 /g surface area is support A. Another sample of the Condea alumina
was impregnated with 8 percent CeO.sub.2 from a cerium nitrate solution
and dried at 120.degree. C. This is support B. A third support was
prepared by impregnating the Condea alumina with lanthanum nitrate to 8
percent La.sub.2 O.sub.3. This is support C. All supports were calcined 3
hours at 1350.degree. F.
EXAMPLE 2
Platinum was impregnated on each support to a level of 500 ppm from a water
solution of the salt (NH.sub.4).sub.6 Pt(SO.sub.3).sub.4 containing 0.2
moles Pt/100 g solution. Each material was dried to prepare catalysts AC,
BC, CC.
EXAMPLE 3
Each of the three catalysts was activated/deactivated by reducing in
flowing hydrogen at 950.degree. F. for 3 hours, cooling, then calcining
for 6 hours at 1350.degree. F. in 50 percent air and 50 percent steam.
EXAMPLE 4
The activity of each oxidation catalyst was tested by adding a small amount
(0.06g) of the promotor after the deactivation in Example 3 to 19.94 g of
a standard commercial FCC catalyst, comprising rare earth exchanged type Y
zeolite, binder, and clay, available as "Super D" from W. R. Grace & Co.
This was followed by placing the mixture in a reactor at 1050.degree. F.,
flowing air over the catalyst, then flowing a 2 percent CO stream at
10,000 WHSV for half an hour, and measuring the CO conversion. The results
of this test are given in Table 1.
TABLE I
______________________________________
Catalyst
AC BC CC
______________________________________
% CO Conversion
53 34 72
ppm Pt on promotor
493 579 497
ppm Pt in mixture
1.479 1.737 1.477
______________________________________
The promotor with cerium (BC) was worse than the control (AC), despite a
slightly higher Pt (BC) level. The La-Pt-alumina of the invention (CC)
showed very good results.
EXAMPLE 5
A support consisting of 25 percent La.sub.2 O.sub.3 on Condea alumina was
prepared by impregnation and calcination similar to Example 1. Pt was
impregnated at a level of 500 ppm in a manner similar to Example 2. The
catalyst was reduced as in Example 3 and deactivated for 15 hours, 5 days,
and 11 days at 1350.degree. F., 50 percent steam, 50 percent air. A sample
of commercial catalyst (CP-3, available from W. R. Grace & Co.),
consisting of 810 ppm Pt on alumina was deactivated using the same
procedure. Each catalyst after each deactivation was tested as in Example
4 with the results in Table II.
TABLE II
______________________________________
CO Conversion, % of Feed
Activation Catalyst: Catalyst:
after 550 ppm Pt/ CP-3 (810 ppm
Deactivation
25% La.sub.2 O.sub.3 /Al.sub.2 O.sub.3
Pt/Al.sub.2 O.sub.3)
______________________________________
5 hrs 64 45
5 days 49 11
11 days 49 23
______________________________________
These results also show the superior performance of the Pt-lanthana-alumina
catalyst of the invention.
My invention will be seen to present several aspects:
(1) The CO-oxidation agent per se (Pt-La-on alumina).
(2) Method of forming the CO-oxidation agent of (1).
(3) Method of oxidizing CO to CO.sub.2 using the CO-oxidation agent of (1).
(4) Composition comprising a hydrocarbon cracking catalyst and the
CO-oxidation agent of (1).
(5) Method of forming the catalyst composition of (4).
(6) Method of oxidizing CO to CO.sub.2 using the catalyst composition of
(4).
More specifically, the composition of (1) may be defined as:
A CO-oxidation catalyst or promoter containing Pt and La.sub.2 O.sub.3 on
alumina substrate, characterized in that
(a) the substrate consists of finely divided particles, average particle
size about 40-120 microns;
(b) the La is impregnated into the substrate, followed by
(c) impregnating the Pt into the La-impregnated substrate;
(d) the La as La.sub.2 O.sub.3 is about 4-30 weight percent of the
catalyst;
(e) the Pt is about 50-1000 ppm of the promoter;
(f) the promoter is cerium-free; and
(g) the substrate has a surface area of at least 45 m.sup.2 /g.
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